During the development of mouse embryos there is an initial set of cleavages resulting in single coherent mass of cells which then undergo compaction and morphogenesis to the first tissue layers. The next morphogenic step is formation of the blastocoel cavity. The blastocyst which consists of outer cells that are called trophectoderm and the inner cells that are called the inner cell mass then expands and by 4 days of gestation hatching begins, and the blastocyst escapes from the zona pellucida, and then implants in the uterine wall. In order for cells to migrate during the expansion of the blastocyst and Reischert's membrane and for trophoblast to invade the uterine tissues orderly and controlled degradation of extracellular matrix macromolecules must occur. The goal of this proposal is to elucidate the role of trophectoderm in the proteolytic mechanisms involved in remodelling of extracellular matrix during cell migration, blastocyst expansion and implantation. The experiments will focus on the metalloproteinases such as collagenase and stromelysin, which have been shown to be important in extracellular matrix degradation in other systems. The metalloproteinases that are synthesized during peri-implantation development in mouse embryos will be determined. The contribution of trophectoderm to the proteolytic potential will be established and the trophectodermal enzymes molecularly cloned. The developmental regulation of these metalloproteinases in cells of the blastocyst will then be determined by immunocytochemical studies, and then by studies on isolated proteinase mRNA as well as RNA in situ in embryos probed with cDNA clones for these proteinases. The regions of the proteinase genes regulating trophectoderm-specific expression will then be determined. Finally the role of trophoblast metalloproteinases in implantation will be determined and its potential regulation by decidual cells examined. These experiments should elucidate the extracellular matrix remodelling functions of the trophectoderm in implantation and embryo development. A better understanding of mechanisms and functions of trophectoderm could lead to an understanding of abnormal trophoblast development that may account for some types of infertility and embryo loss early in pregnancy, and may provide a basis for improving the rate of successful pregnancy after in vitro fertilization.